> Yes you need to look into the packet a little bit to hash well, but this > isn't a difficult operation either (compared to holding a full table and > doing longest prefix lookups at any rate).
As far as I understand, it's not really correct to compare difficulty of these two operations, since they are performed by two different units inside the chip. While label lookup instead of full IP table can dramatically simplify the lookup unit's life, the unit, which inspects packets and extracts bits from them, must be still quite complex even for label-only router. Hashing ALU's life is not a peace of cake either. Say, EX series PFE use only 6-bit seeds to construct hash on them. In case you want to push a whole 20-bit label to the hash seed, I'm afraid, you'll need more bits in ALU registers, more cycles or something else. Add here the need to perform double label lookups and push/pop labels for things like facility protection, and you'll have not that simple PFE, not that simple software to work with it, and not that cheap product overall. On the other hand, yes, Juniper could throw all that features away, just put back ISIS-TE, LDP and few other MPLS control plane things back to JUNOS for EX series and have a cheap and cheerful LSRs for BGP-free core. But, Richard, I can't even imagine the words you'd use, if someone tried to sell you such a product ;) FWIW EX8200 is actually kinda bad at multipath hashing too. I'm more or less sure, so is any cheap PFE used in ethernet switches. I've heard (please correct me if I'm wrong), that the $1 per bucket ASICs, used in switches, are VLIW, which is hard to reprogram. While the more expensive ones, custom developed for routers, are rather sort of more flexible tiny MIMD computers with asynchronously working units inside. _______________________________________________ juniper-nsp mailing list juniper-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/juniper-nsp